JP2010016664A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera capable of correcting the face region of a person to proper brightness, and maintaining gradation of the background. <P>SOLUTION: In the camera comprising: an imaging means for imaging picture data; a gamma correction part for performing gamma correction for the picture data; a face region detecting means for detecting the face region from the picture data; a photometric means for performing photometry of the face region of the person detected by the face region detecting means as a photometric area; an exposure controlling means for calculating a target exposure amount on the basis of the output result of the photometric means and controlling an exposure value on the basis of the calculated target exposure amount; and a gamma correction controlling part for determining gradation characteristic corresponding to the target exposure amount, the gamma correction part is controlled on the basis of the gradation characteristic determined by the gamma correction controlling part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus.

  As a background art in this technical field, there is JP-A No. 2007-180892 (Patent Document 1). In this publication, “a camera includes a face detection circuit, a gamma correction control unit, and an image signal processing circuit. The face detection circuit detects a face from an input image signal, and includes a face including the detected face. The gamma correction control unit determines a gradation characteristic based on the luminance change evaluation value calculated by the face detection circuit, and the image signal processing circuit calculates the gradation determined by the gamma correction control unit. The input image signal is gamma-corrected based on the characteristics. "

JP 2007-180892 A

  Digital cameras for taking still images and moving images have become widespread, and anyone can easily obtain good images. Since the most frequently photographed subject in such images is a person, an increasing number of cameras are equipped with face recognition / optimization functions that automatically recognize human faces and optimize camera settings. Yes.

  The face recognition function installed in such a camera collates the pattern stored in the camera memory in advance with the input image, and detects the area where the face exists (hereinafter referred to as “face area”) on the screen. To do. The information in the detected face area includes the position of the area, the photometric quantity, the color, and the like. Based on such information, appropriate processing is automatically performed when the detected face area is photographed. Here, examples of appropriate processing include the following. Perform processing so that the face area has the appropriate brightness, focus on the face area with priority, adjust the white balance so that the face area has the appropriate color, and set the color signal to improve skin tone Change.

  Here, the technique of automatically correcting the face area to the appropriate brightness, which is the first of the appropriate processes, is highly necessary for the user. When shooting a person, there are often situations where the brightness difference between the background and the person increases, such as backlighting. In such cases, the brightness of the person is greatly affected by the brightness of the background. It may not be a thing. Further, it is conceivable to manually correct this so as to obtain an appropriate brightness. However, manual correction is complicated, and correction is difficult for a general user.

  On the other hand, as a technique for automatically correcting the face area to an appropriate brightness, exposure control (iris, shutter, AGC circuit (automatic gain circuit)) is performed according to the target exposure amount calculated based on the photometric result of the face area. There is a method of changing the appropriate control). However, since the exposure control value is a value that uniformly changes the brightness of the entire captured image, the brightness of the face area is appropriate, but the brightness of the background is inappropriate, and white stripes and black blurring occur. There is.

  A method of changing gamma correction control according to the target exposure calculated based on the photometric amount of the face area as a technology that automatically corrects the face area to an appropriate brightness and prevents white background and black blur in the background There is. The gamma correction control is a technique for changing the gradation characteristics of the photographed image. By appropriately controlling this, the brightness of the face area and the gradation of the background can be made compatible.

  As a technique for changing the gradation characteristics by gamma correction control according to the information on the face area detected by the face recognition function, for example, “Patent Document 1” is known. According to “Patent Document 1”, it is possible to obtain a proper brightness even when there is a luminance difference in the face region by calculating a luminance difference in the face region and applying a gradation characteristic corresponding to the difference. Technology. However, in this method, only the luminance difference of the face area is used as the criterion for gamma correction control, and therefore, the reproducibility of the gradation of the background luminance is not considered much.

  As described above, in order to achieve both human face brightness and background gradation when shooting a person, the exposure control and gamma correction control are appropriately controlled based on the face area information. It is necessary to set an exposure control value and gradation characteristics corresponding to the exposure control value.

  Since the conventional face recognition / optimization function uses only the luminance difference of the face area as a criterion for gamma correction, it does not consider the reproducibility of the background luminance gradation.

  An object of the present invention is to provide an imaging device with high image quality. For example, it is to provide an imaging device capable of correcting a face area to an appropriate brightness and maintaining a background gradation.

  In order to solve the above object, the configuration described in the claims is adopted.

  According to the present invention, it is possible to provide an image pickup apparatus with high image quality. For example, by appropriately setting the exposure control value and the gradation characteristics, it is possible to maintain the gradation of the background while appropriately correcting the brightness of the face area. Further, for example, since the gradation characteristics can be changed depending on the size of the face area, it is possible to provide a camera that retains the optimum gradation characteristics depending on the shooting scene.

  Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of a camera according to the present invention, wherein 1 is a camera lens, 2 is an iris, 3 is an image sensor, 4 is an AGC circuit (automatic gain control circuit), and 5 is an A / D converter. 6 is an image processing circuit, 7 is a gamma correction unit 7, 22 is a gamma correction control unit, 8 is an encoder, 9 is a D / A conversion circuit, 10 is a face detection unit, 11 is a face area area calculation unit, and 12 is Exposure control unit, 13 photometry unit, 14 target exposure calculation unit, 15 memory, 16 target exposure threshold, 17 AGC control unit, 18 iris control unit, 19 lens control unit, 20 shutter control unit, Reference numeral 21 denotes a shutter.

  In FIG. 1, a shutter control unit 20 controls the shutter 21 when the shutter button of the camera is pressed. The camera lens 1 includes a focus lens and a zoom lens, and is controlled by the lens control unit 19. The iris 2 is controlled by the iris control unit 18 and adjusts the amount of incident light from the camera lens 1. The imaging device 3 is a CMOS imaging device or the like, and photoelectrically converts a subject image formed on the imaging surface by the camera lens 1 and outputs an analog imaging signal (analog imaging signal). The AGC circuit 4 is controlled by the AGC control unit 17 and amplifies the analog imaging signal to a predetermined signal level. The A / D conversion circuit 5 converts the analog imaging signal amplified by the AGC circuit 4 into a digital imaging signal (digital imaging signal). The image processing circuit 6 includes a gamma correction unit 7 and a gamma correction control unit 22, generates a digital luminance signal and a digital color signal from a digital imaging signal that is an output of the A / D conversion circuit 5, and performs gamma correction processing and edge enhancement. Various signal processing such as processing, noise reduction processing, and white balance are performed. The encoder 8 generates a digital television signal conforming to a standard television system such as the NTSC system from the digital luminance signal and the digital color signal output from the image processing circuit 6. The digital television signal is recorded on a recording medium such as an optical disk (for example, BD (Blu-ray Disc), DVD), a hard disk (HDD), or a semiconductor memory (built-in / detachable) by a recording / reproducing circuit (not shown). Recorded and played back. The D / A conversion circuit 9 converts the digital television signal into an analog standard television signal.

  The face detection unit 10 detects a face detection area included in the image signal output from the image sensor 3 in the following procedure. First, the face detection unit 10 extracts a skin color region from the image signal input to the image processing circuit 6. Next, contour extraction is performed on the previously extracted region based on the luminance change, and it is confirmed whether or not both eyes and mouth exist in an arrangement that is relatively located between both eyes and mouth. When both eyes and mouth exist, a rectangular area surrounding the area is detected as a face area. In addition, the face area calculation unit 11 calculates the ratio of the face area to the shooting screen by the following formula. When the number of effective pixels of the image sensor 3 at the time of shooting is d1, and the number of pixels in the face area is d2, the face area S is S = d2 / d1. When a plurality of face areas are detected, for example, the sum of the plurality of face areas is set as the number of pixels d2 occupying the face area.

  The exposure control unit 12 includes a photometry unit 13 and a target exposure calculation unit 14, calculates a target exposure amount based on a photometric result obtained by measuring the image signal of the face area by the photometry unit, and performs exposure control according to the target exposure amount. After determining the value, the AGC control unit 17, the iris control unit 18, and the shutter control unit 20 are controlled so that the digital imaging signal input to the image processing circuit 6 becomes a value corresponding to the exposure control value.

  FIG. 3 is a diagram showing an example of the relationship between the photometric result of the face area and the target exposure amount I. Target exposure determination values c1 and c2 are set for the target exposure amount. Details will be described later.

  FIG. 4 is a view showing an example of the relationship between the target exposure amount I and the exposure control value R. When the target exposure amount I is larger than c2 and smaller than c1, the exposure control value R changes dynamically according to the target exposure amount I. When the target exposure amount I is c1 or more, the exposure control value R is fixed to the exposure control maximum value r1, and when the target exposure amount I is c2 or less, the exposure control value R is fixed to the exposure control minimum value r2.

  FIG. 5 is a diagram showing the relationship between the target exposure amount I and the gamma coefficient G used for determining the gradation characteristics. In the present invention, in order to relate the target exposure amount I to the gradation characteristic, first, a gamma coefficient G corresponding to the target exposure amount I is calculated, and the gradation characteristic is determined based on the gamma coefficient G. ing. For example, when the target exposure amount I is larger than c2 and smaller than c1, the gamma coefficient G is fixed to g1, which is the same value as when the face detection unit does not detect a face area (hereinafter referred to as normal time). When the target exposure amount I is c1 or more or c2 or less, the gamma coefficient G is dynamically changed according to the target exposure amount I and the area of the face area.

  6 and 7 show examples of gradation characteristics according to the gamma coefficient G. FIG. FIG. 6 shows a case where the gamma coefficient G is larger than the normal coefficient g1 (ga area shown in FIG. 5). As the gamma coefficient G increases, L3, L4, L5,. The gradation characteristics are changed so as to widen the gradation of the intermediate portion. FIG. 7 shows a case where the gamma coefficient G is smaller than the normal coefficient g1 (gb region shown in FIG. 5). As the gradation characteristic G becomes smaller, L3, L6, L7. The gradation characteristics are changed so as to narrow the gradation of the intermediate portion.

Next, the operation of the embodiment according to the present invention will be described.
The camera lens 1 forms a subject image on the imaging surface of the image sensor 3. The image pickup device 3 outputs an analog image pickup signal by photoelectrically converting an optical signal corresponding to the brightness of the subject image into an electric signal. The analog imaging signal is amplified to a predetermined signal level by the AGC circuit 4, converted to a digital imaging signal by the A / D conversion circuit 5, and supplied to the image processing circuit 6.

  At this time, when the face detection unit 10 detects a face area with respect to the digital image pickup signal input to the image processing circuit 6, processing is performed according to the processing procedure shown in FIG. 2 so that the face area has appropriate brightness. First, the image signal for the face area detected by the face detection unit 10 is measured by the photometry unit 13 provided in the exposure control unit 12, and based on the photometry result, the target exposure calculation unit 14 sets the target exposure amount I. Is calculated (S2). For the relationship between the photometric result and the target exposure amount I, for example, the characteristics shown in FIG. 3 may be used.

  If the target exposure amount I is smaller than the target exposure determination value c1 and larger than the target exposure determination value c2 (S3), the exposure control unit 12 calculates an exposure control value R based on the target exposure amount I, and this exposure control. Using the value R, the iris control unit 18, the shutter control unit 20, and the AGC circuit control unit 17 are controlled. On the other hand, the gamma correction control unit 22 sets g1 as a gamma coefficient in the gamma correction unit 7. This gamma coefficient g1 is the same value as in normal times, and is a fixed value as shown in FIG. Using this gamma coefficient g1, the gamma correction unit 7 performs gamma correction processing on the digital imaging signal (S4). This is a case where the correction range of the brightness of the face area is small, and in this case, even if the brightness of the entire photographed image is uniformly changed by the exposure control value, there is a low possibility that the background gradation will be lost. For this reason, the gamma correction control is the same as usual, and by correcting the brightness only with the exposure control value R, the brightness of the face area can be set to the optimum setting while making the background gradation appropriate. It becomes possible.

  Next, when the target exposure amount I is larger than the target exposure determination value c1 (S5), the exposure control unit 12 fixes the exposure control value R to the exposure control maximum value r1, and the iris control unit 18, shutter control unit 20, and AGC. Set in the circuit control unit 17. On the other hand, the gamma correction control unit 22 sets gradation characteristics according to the target exposure amount I and the face area area S, and the gamma correction unit 7 performs gamma correction processing of the digital imaging signal based on the gradation characteristics (S6). ). This is the case, for example, when the person who is the subject appears in a strong backlight condition, and it is necessary to correct the brightness of the face area significantly, and if this is corrected only with the exposure control value R, the background may be overexposed. There is sex. For this reason, the exposure control value R is fixed to a value (exposure control maximum value r1) that does not cause white background. Then, brightness correction that is insufficient for exposure control is performed by changing the gradation characteristics by gamma correction control. As a result, it is possible to maintain the gradation of the background while making the brightness of the face appropriate.

  Further, when setting the gradation characteristics, it is possible to set more appropriate gradation characteristics by simultaneously performing the control according to the area of the face region as shown below.

  First, when the face area S is smaller than the predetermined threshold k (S8), the gamma correction control unit 22 sets L3 that is close to the normal gradation characteristic (S9). This is a case where a person is reflected in a backlit state and a relatively large proportion of the background occupies the screen. At this time, it is considered that the user attaches more importance to the gradation of the background. However, when the gradation characteristic according to the brightness of the face area is applied, the background may be overexposed. In order to prevent this, gradation characteristics close to normal are applied.

  Next, when the face area S is larger than the threshold value k and smaller than the predetermined threshold value m (S10), the gamma correction control unit 22 sets L4, which is a slightly expanded gradation in the intermediate part (S11). This is a case where a person is reflected in a backlight state and the ratio of the background to the person occupying the screen is half. This is a scene where you want to keep both the background and the gradation of the person. In this case, gradation characteristics that emphasize the brightness of the face area as compared with the previous case are applied to make the face area appear brighter. However, the gradation is set so as not to be overexposed so that the background is not overexposed.

  Finally, when the face area S is larger than the predetermined threshold value m (S10), the gamma correction control unit 22 sets L5, which greatly increases the gradation of the intermediate part (S12). This is the case when a person is reflected in a backlight state and the proportion of the person in the screen is relatively large. At this time, since it is considered that the user places more importance on the gradation of the person, a gradation characteristic that matches the brightness of the face area is applied.

  Next, when the target exposure amount I is smaller than the predetermined threshold value c2 (S5), the exposure control unit 12 calculates an exposure control value based on the target exposure threshold value c2, and the iris control unit 18, shutter control unit 20, and AGC circuit control unit. On the other hand, the gamma correction control unit 22 sets gradation characteristics corresponding to the target exposure amount I and the face area area S, and the gamma correction unit 7 performs gamma correction processing of the digital image pickup signal based on the gradation characteristics. (S13). This is the case, for example, when a person appears in a dark background with a strong spotlight, and when correcting by greatly reducing the brightness of the face area. If corrected, the background may be blackened. For this reason, the exposure control value R is fixed to a value (exposure control minimum value r2) at which the background does not black out. Then, by changing the gradation characteristics by the gamma correction control, the brightness that cannot be lowered by the exposure control is compensated. As a result, the gradation of the background can be maintained while the brightness of the face is made appropriate. Further, when setting the gradation characteristics, it is possible to set more appropriate gradation characteristics by simultaneously performing control according to the area of the face area as shown below.

  First, when the face area S is smaller than the predetermined threshold k (S15), the gamma correction control unit 22 sets L3 that is close to the normal gradation characteristic (S16). This is the case when a person is reflected in a spotlight on a dark background. If the background occupies a relatively large percentage of the screen in this way, the user may think that the background gradation is more important, but if the gradation characteristics that match the brightness of the face area are applied, the background will be blackened. There is. In order to prevent this, gradation characteristics close to normal are applied.

  Next, when the face area S is larger than the threshold value k and smaller than the predetermined threshold value m (S17), the gamma correction control unit 22 sets L6, which is a slightly narrowed gradation of the intermediate portion (S11). This is the case when a person appears in a spotlight in a dark background and the ratio of the background to the person occupying the screen is half. This is a scene where you want to keep both the background and the gradation of the person. In this case, gradation characteristics that emphasize the gradation of the face area than in the previous case are applied, and the face area is darkened to suppress white stripes. However, the setting is made so that the gradation is not lowered too much so that the background does not blur.

  When the face area S is larger than the predetermined threshold value m (S17), the gamma correction control unit 22 sets L7, which is a much narrower gradation of the intermediate part (S12). This is a case where a person is captured in a spotlight and a relatively large proportion of the person occupies the screen. At this time, since it is considered that the user places more importance on the gradation of the person, the face area is made darker and the gradation characteristics are set such that the white stripe is completely suppressed.

  The target exposure determination value c1 is set in advance so as to prevent the gradation of a signal with high luminance from being lost in the digital image pickup signal input to the image processing circuit 6. Further, the target exposure determination value c2 is set in advance so that the gradation of the low luminance signal among the digital image pickup signals input to the image processing circuit 6 is not destroyed. These target exposure thresholds c1 and c2 are values set at the manufacturing stage as camera devices, but may be set manually according to user preference. For example, on the display screen provided in the camera, the degree of exposure control in the face area may be selected. If it is selected to increase the degree of exposure control in the face area, the target exposure determination value c1 is increased and c2 is decreased. In this case, the exposure control value is dynamically set in a wide range of the target exposure amount based on the photometric result of the face area. On the other hand, when it is selected to weaken the exposure control level in the face area, the target exposure determination value c1 is decreased and c2 is increased. In this case, the exposure control value is dynamically set within a narrow range of the target exposure amount based on the photometric result of the face area.

  The predetermined threshold k used for the determination of the face area is a threshold when the ratio of the face area to the screen is small and the background occupies most of the screen, and m is a time taken when a person's bust shot is taken. Threshold. These threshold values k and m are values set at the manufacturing stage as camera devices, but may be set manually according to user preference. For example, the degree of determination of the face area area may be selected on the display screen of the camera. When the selection is made to increase the degree of determination of the face area, the threshold values k and m are decreased, and the change in the gradation characteristics according to the face area is increased. On the contrary, when the selection is made to weaken the degree of determination of the face area, the threshold values k and m are increased, and the change in the gradation characteristics according to the face area is reduced.

  Further, the gradation characteristics controlled by the gamma control unit may include not only luminance gradation characteristics but also color gradation correction. If only the luminance gradation correction is changed, the composition ratio between the color and the luminance may change depending on the scene, and the color of the captured image may be lightened or darkened. By changing luminance and color gradation correction at the same time, the color of the captured image can be maintained at an appropriate color.

  In addition, each process such as a noise removal process, a signal enhancement process, and a color difference signal process may be adaptively changed according to a photometric result calculated by the photometric unit and a gradation characteristic set by the gamma correction control unit 22. When the gradation characteristics change, the way noise is generated may be different. By applying adaptive processing such as applying signal enhancement processing when noise is reduced due to changes in tone characteristics and increasing noise removal processing when noise increases, higher-quality images can be obtained. Is obtained.

  In the above embodiment, a face is detected, but the present invention can be applied to a specific subject other than the face by the same configuration and operation as in the above embodiment. In this case, techniques for detecting various specific subjects can be used, and detailed description thereof is omitted.

  The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to add, delete, and replace other alternative configurations for a part of the configuration of the embodiment.

  In addition, each of the above-described configurations may be configured such that some or all of them are configured by hardware, or are implemented by executing a program by a processor. Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

The block block diagram which shows one Embodiment of the camera by this invention The figure explaining the process which correct | amends a face area to appropriate brightness, without destroying the gradation of a background The figure which shows the target exposure amount with respect to the photometry result of the face area | region in one Embodiment of this invention. The figure which shows the exposure control value with respect to the target exposure amount in one Embodiment of this invention. The figure which shows the gamma coefficient with respect to the target exposure amount in one Embodiment of this invention. The figure showing the change of the gradation characteristic when the gamma coefficient increases in one embodiment of the present invention. The figure showing the change of the gradation characteristic when the gamma coefficient in one embodiment of this invention decreases.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Camera lens, 2 ... Iris, 3 ... Image sensor, 4 ... AGC circuit (automatic gain control circuit), 5 ... A / D conversion circuit, 6 ... Image processing circuit , 7 ... Gamma correction unit, 8 ... Encoder, 9 ... D / A conversion circuit, 10 ... Face detection unit, 11 ... Face region area calculation unit, 12 ... Exposure control unit , 13 ... Metering section, 14 ... Target exposure calculation section, 15 ... Memory, 16 ... Target exposure threshold, 17 ... AGC control section, 18 ... Iris control section, 19 ... Lens control unit, 20 ... shutter control unit, 21 ... shutter, 22 ... gamma correction control unit

Claims (7)

An imaging device including a gamma correction unit that performs gamma correction on an input image,
Imaging means for inputting image data according to the subject;
A face detection means for detecting a face from the input image;
Metering means for metering the face of the person detected by the face detecting means as a metering area;
Exposure control means for calculating a target exposure amount based on a photometric result of a person's face of the photometry means, and calculating an exposure control value based on the calculated target exposure amount;
A gamma correction control unit that determines gradation characteristics according to a target exposure amount;
With
The gamma correction unit performs gamma correction on the input image using the gradation characteristics determined by the gamma correction control unit;
An imaging apparatus characterized by the above. In claim 1,
An imaging apparatus comprising: a memory storing data necessary for image processing, wherein a target exposure amount determination value and an exposure control threshold value that can be set are stored in the memory. In claim 2,
The gamma correction control means makes the gradation characteristic when the target exposure amount is within the range of the target exposure determination value different from the gradation characteristic when the target exposure amount is outside the range of the target exposure determination value;
An imaging apparatus characterized by the above. In claim 1,
The face detection means comprises a face area calculation means for calculating the area of the face area including the detected face;
An imaging apparatus characterized by the above. In claim 4,
The gamma correction control means sets a gradation characteristic according to the area of the face area calculated by the face area area calculation means;
An imaging apparatus characterized by the above. Imaging means for imaging a subject and outputting image data;
Detection means for detecting a specific subject from image data output by the imaging means;
Exposure control means for performing exposure control on the imaging means within a range determined by a predetermined determination value using image data corresponding to a specific subject detected by the detection means;
Gamma correction means for performing gamma correction on the image data output by the imaging means;
Control is performed so that the gradation characteristics of the gamma correction performed by the gamma correction unit differ between when the exposure control unit performs exposure control with the determination value and when the exposure control unit performs exposure control within the range. Control means;
An imaging apparatus comprising: In claim 6,
The detection means includes specific subject area calculation means for calculating a ratio of the area of the image data corresponding to the specific subject to the entire image data,
When the exposure control unit performs exposure control with the predetermined determination value, the control unit performs a gamma correction gradation characteristic performed by the gamma correction unit according to the ratio of the area calculated by the specific subject area calculation unit. Control to be different,
An imaging apparatus characterized by the above.

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